Organo Photoinduced Decarboxylative Alkylation of Coumarins with N-(Acyloxy)phthalimide

A metal-free and mild, photoinduced decarboxylative 4-position alkylation of coumarins has been reported. Photoinduced single electron transfer has been initiated by utilizing the visible-light absorptivity of Eosin Y for a reductive generation of alkyl radicals from N-(acyloxy)phthalimide esters. Depending on the nature of N-(acyloxy)phthalimide esters (primary, secondary, and tertiary carboxylic acid derived), several saturated and unsaturated C-4 alkylated coumarins were synthesized. Both control experiments and photophysical studies supported a radical based mechanism for the selective alkylation.